---

name: app description: Use when working on the mobile app (packages/app). Covers Expo, React Native, expo-router navigation, NativeWind styling, React Query data fetching, translations, and mobile-specific patterns.

Mobile App Development Guide

You are working on the 100cims mobile app (packages/app), an Expo React Native application for mountaineering.

Key Files

Stack

• Expo SDK 54 with React Native 0.81 (new architecture enabled)
• expo-router 6 for file-based navigation
• NativeWind 4 for styling (Tailwind CSS)
• React Query 5 for server state
• React Intl for i18n (en, ca, es)

Directory Structure

• /app/: expo-router screens (file-based routing)
• /domains/: Feature-specific business logic
• /hooks/: Shared React hooks
• /lib/: Utility functions (api-client, auth, dates, images, location, validation)
• /components/: Reusable UI components
• /translations/: i18n message files
• /types/: Shared TypeScript types (api.ts auto-generated, mountain.ts, etc.)

Domain Pattern

Each domain folder typically contains:

• *.api.ts: React Query hooks for API calls
• *.utils.ts: Domain-specific utilities
• *.types.ts: TypeScript types (optional)

Example: /domains/user/user.api.ts exports useUser(), useUpdateUser(), etc.

Shared Hooks

Shared Utilities

Shared Types

Key Patterns

Using Shared Hooks

Copy// Image picker with optimization
import { useImagePicker } from '@/hooks/use-image-picker';

const { imageUri, imageBase64, hasChanged, pickImage, reset } = useImagePicker({
  initialUri: existingImageUrl,
});

// Mountain selection state management
import { useMountainSelection } from '@/hooks/use-mountain-selection';

const {
  selectedMountainIds,
  newMountains,
  selectedMountainsForDisplay,
  totalMountainCount,
  handleSelectionChange,
  handleAddNewMountain,
  handleRemoveNewMountain,
} = useMountainSelection({ allMountains });

Form Validation

Copyimport { validateMountainForm } from '@/lib/mountain-validation';

const validation = validateMountainForm({ name, location, height, latitude, longitude }, intl);
if (!validation.valid) {
  return Alert.alert(validation.error);
}
// Use validation.data.name, validation.data.height (parsed numbers), etc.

API Calls

Copy// Use openapi-fetch client from lib/api-client.ts
import apiClient from '@/lib/api-client';
import { useQuery } from '@tanstack/react-query';

export const useUser = (userId: string) => {
  return useQuery({
    queryKey: ['user', userId],
    queryFn: async () => {
      const { data, error } = await apiClient.GET('/api/user/{id}', {
        params: { path: { id: userId } }
      });
      if (error) throw error;
      return data;
    }
  });
};

Infinite Scroll with Pagination

Copyimport { useInfiniteQuery } from '@tanstack/react-query';

export const useItemsList = () => {
  return useInfiniteQuery({
    queryKey: ['items', 'list'],
    initialPageParam: 1,
    queryFn: async ({ pageParam }) => {
      const { data, error } = await apiClient.GET('/api/items', {
        params: { query: { page: pageParam, limit: 50 } },
      });
      if (error) throw error;
      return data.message;
    },
    getNextPageParam: (lastPage) => {
      if (lastPage?.pagination?.hasMore) {
        return lastPage.pagination.page + 1;
      }
      return undefined;
    },
  });
};

// In component:
const { data, fetchNextPage, hasNextPage, isFetchingNextPage } = useItemsList();
const items = data?.pages?.flatMap((p) => p?.items ?? []) ?? [];

<FlatList
  data={items}
  onEndReached={() => hasNextPage && !isFetchingNextPage && fetchNextPage()}
  onEndReachedThreshold={0.5}
  ListFooterComponent={isFetchingNextPage ? <ActivityIndicator /> : null}
/>

Authentication

• JWT stored in AsyncStorage
• setAuthToken(token) in lib/api-client.ts sets Authorization header
• Protected routes check auth state in _layout.tsx

Styling with NativeWind

Copy<View className="flex-1 bg-white dark:bg-gray-900">
  <Text className="text-lg font-bold text-gray-900">Title</Text>
</View>

Navigation

Copyimport { router } from 'expo-router';

// Navigate
router.push('/user/123');

// With params
router.push({ pathname: '/mountain/[id]', params: { id: '456' } });

Translations (CRITICAL)

All user-facing strings MUST use intl.formatMessage - never hardcode text.

Copyimport { useIntl } from 'react-intl';

const { formatMessage } = useIntl();

// Simple string
const title = formatMessage({ defaultMessage: 'Settings' });

// In JSX
<ThemedText>{intl.formatMessage({ defaultMessage: "Save changes" })}</ThemedText>

// With FormattedMessage component
import { FormattedMessage } from 'react-intl';
<FormattedMessage defaultMessage="Welcome back" />

Translation Workflow:

1. Add strings in code using defaultMessage (English text)
2. Run extraction: yarn translations:extract
3. Run compilation: yarn translations:generate
4. English (translations/en.json) is auto-generated
5. Manually copy new keys to translations/ca.json (Catalan) and translations/es.json (Spanish)
6. Translate the values in ca.json and es.json

Translation Files:

• translations/raw-en.json - Extracted messages (intermediate)
• translations/en.json - Compiled English (used by app)
• translations/ca.json - Catalan translations (manual)
• translations/es.json - Spanish translations (manual)

Common Tasks

Add New Screen

1. Create file in /app/ (e.g., /app/settings.tsx)
2. Export default React component
3. File name becomes route path

Add API Integration

1. Ensure backend types are current: yarn generate-api-types
2. Create domain API file or add to existing
3. Use React Query for data fetching
4. Handle loading/error states

Add/Update Translations

1. Use intl.formatMessage({ defaultMessage: "English text" }) in code
2. Run yarn translations:extract to extract all messages
3. Run yarn translations:generate to compile English
4. Copy new keys from en.json to ca.json and es.json
5. Translate the values in ca.json and es.json

Add Native Module

Copynpx expo install <package-name>

May need to rebuild: npx expo prebuild --clean

Environment Variables

Must prefix with EXPO_PUBLIC_ to access in app:

• EXPO_PUBLIC_API_URL: Backend URL
• EXPO_PUBLIC_REACT_ANALYTICS_KEY: Analytics key
• OAuth client IDs for Google/Apple

Debugging

Common Issues

• Type errors: Regenerate API types with yarn generate-api-types
• Navigation issues: Check expo-router file structure
• Styling not applying: Verify NativeWind babel config, global.css import
• OAuth not working: Check google-services.json, Apple config in app.config.ts

Helpful Commands

Copynpx expo start --clear          # Clear cache
npx expo-doctor                 # Diagnose issues
npx uri-scheme list             # Check deep linking

Build & Deploy

Copyeas build --profile development  # Dev build with expo-dev-client
eas build --profile preview      # Internal preview
eas build --profile production   # Production release

See eas.json for build profiles.